In situ Assessment of the Transport and Microbial Consumption of Oxygen
in Ground Water, Cape Cod, Massachusetts

ABSTRACT

Oxygen is a key ground-water constituent, controlling both the geochemistry
and microbiology of an aquifer. Accordingly, aerobic respiration, the microbial
metabolic process that consumes oxygen, is fundamentally important to the
overall functioning of the aquifer. However, despite its significance, few
studies have directly examined this process in the subsurface. This study
has used several different approaches to investigate oxygen consumption on
several different scales in parts of a large (> 5 kilometers) plume of dilute
sewage contamination in a sand and gravel aquifer on Cape Cod, Mass. First,
oxygen concentration profiles and stable isotope ratios were used to infer
the net effect of aerobic respiration on the aquifer scale. Second, natural
gradient tracer tests were used at an intermediate scale to measure in situ
rates of aerobic respiration within different contours of the ground-water
oxygen gradient. Third, two different types of laboratory incubations using
aquifer core material, potential electron transport activity (ETS) and oxygen
uptake activity, were used for small-scale examination of the process. The
latter methods yield estimates of rates and kinetic parameters, which can
be compared with the tracer test and isotope results. The sum of these approaches
views the aquifer within the context of a subsurface ecosystem, integrating
the combined effects of the hydrology, geochemistry and microbiology on the
process of oxygen consumption.